1. Field of the Invention
The present invention relates generally to the fields of vehicle safety and compressed natural gas and more particularly to safety system related to fueling vehicles powered by compressed natural gas.
2. Description of the Prior Art
Natural gas is becoming an abundant resource in the United States and several other countries. It is estimated that the natural gas reserves of the U.S. exceed the oil reserves of Saudi Arabia in terms of years of energy supply.
In order to utilize this resource effectively, and to replace crude oil, natural gas must be used in vehicles. Many fleet operators are switching their vehicles to natural gas since, with minor modifications, internal combustion engines run very well on natural gas.
Natural gas is typically supplied in two different forms: 1) as a compressed gas, and 2) as a liquefied gas. While more efficient in terms of the amount of gas that can be supplied in a single tank, liquefied gas is very dangerous to handle and requires highly specialized equipment to fuel with it and actually use it. On the other hand, compressed natural gas is relatively easy to fuel with and to utilize. Compressed natural gas can be supplied in pressure bottles a pressures between 3000 psi and 4000 psi. It is very well known in industry how to handle and fill such bottles. A natural gas “gas station” can fill a vehicle tank (pressure bottle) in just a few moments using fill techniques similar to high pressure air. A vehicle tank containing 100-200 cu. feet of natural gas at a pressure of 3500 psi is typically not more dangerous than a typical automobile's gasoline tank. The tank can be shielded from direct impact in an accident.
Many households and businesses in the U.S. have piped in natural gas for cooking and, in many cases, heating. Most Americans own at least one car or other vehicle, with many households owning several vehicles. This combination immediately suggests the possibility of filling a natural gas vehicle at home during the night for use the next day, or filling at the location of a small business. Because even a large compressed natural gas tank will not last as long between refills as a typical gasoline tank, it will become a very convenient to refill it during the night. The vehicle owner can also use natural gas filling stations; however, these will probably be more convenient for extended trips. Most people would prefer not to have to wait 5-10 minutes at a gas station to fill their vehicle. While exchangeable tanks are also possible, these require considerably more logistics and handling than a simple fixed onboard tank. Even with exchangeable tanks, the vehicle owner would still probably have to wait considerably longer to get a refill at a station than they currently do with gasoline.
At the present time, at least one car manufacturer is supplying a compressed natural gas vehicle and a home compressor to fill it. National fire codes currently prevent large gas storage tanks in homes or compressors that fill at fast rates. Given present standards, the home compressor will be directly attached to the vehicle via a high pressure hose, and the vehicle will take several hours to fill (depending on the size of the onboard tank). Again, this will be very conveniently accomplished during the night. The same arrangement can be used at small businesses, especially those with fleets of vehicles.
However, with numerous individuals filling natural gas vehicles in their garages at night or at their business locations, the potential for a very serious type of accident increases dramatically—namely what is called a drive-off accident. This is where the driver tries to drive away with the high pressure filling hose still attached to the vehicle. Such an accident in a home garage could be catastrophic if the fitting or valve on the vehicle is damaged, or if the compressor is pulled away from the home natural gas source. In either case, a considerably amount of gas could escape into the garage causing a fire or explosion danger. Also, even a “soft” drive-away accident, one where the driver stopped before breaking the hose or fitting could stress the fill hose and possibly cause small, very hard to detect, gas leaks. Such small leaks could result in the garage being filled with gas by morning.
Natural gas contains mostly methane and is thus lighter than air. Natural gas leaking in a garage will fill the garage from top to bottom. An explosive mixture for natural gas and air is between around 5% (for pure methane) and around 15-20%. Many garages contain furnaces and water heaters having open flames. As natural gas fills a garage, it can be easily ignited by a furnace or a water heater on a raised pedestal (fire codes require open flame devices in garages to mounted on pedestals to avoid gasoline vapor that might collect along the floor from a car gasoline leak). This is an ideal situation for a garage explosion. Hence anything that has the possibility of causing the release of natural gas or of causing a gas leak becomes a large danger. A drive-away accident is such an event.
Some techniques have been reported in the art to prevent a gasoline vehicle from starting at a gasoline station if the fill nozzle is still in the gas tank inlet. Among these are U.S. Published Application No. 2002/0162601 and U.S. Pat. No. 5,720,327. Other techniques have been invented to prevent pumping gasoline or other fuel if the fill hose is not in the fill inlet. Among these are U.S. Published Application No. 2008/0290152 and U.S. Pat. No. 4,227,497.
While these prior art techniques are useful for gasoline, they do not solve the problems associated with home or business filling a vehicle with high pressure compressed natural gas. In particular, a compressed natural gas tank is filled to a very high pressure (between 3000 and 4000 psi). A leak or disconnect of a fitting or valve on such a pressure vessel can cause a tremendous pressure explosion that can act like a bomb (this can happen with any compressed gas including air). Also, a very small leak at high pressure can cause a large quality of gas to escape. For example, an exploding tank can send metal fragments in all directions with enough force to penetrate the house and the driver's compartment of the vehicle. This can happen before there is any fire. After that, the tiniest spark could ignite the now explosive and highly flammable gas cloud reducing the house or business to rubble. Even a quick-disconnect hose does not typically solve the problem since the driver may attempt to drive away very quickly still damaging the fittings, tank, hose, compressor and/or natural gas supply.
It would be very advantageous to have doubly or triply redundant system and method that prevents the driver from ever starting the vehicle when the filling hose is attached and a safety valve is not in the correct position.